Hip Joint Anatomy: The Acetabular Fossa and Ligament of the Head of the Femur

What depression is the site where a femoral ligament attaches to the acetabulum?

The depression in the acetabulum where a specific femoral ligament—the ligament of the head of the femur (ligamentum teres femoris)—attaches is known as the acetabular fossa.

Understanding the Hip Joint Anatomy

The hip joint is a critical ball-and-socket synovial joint, renowned for its combination of stability and mobility. Formed by the articulation of the head of the femur (thigh bone) and the acetabulum of the pelvis, it supports the weight of the upper body and facilitates a wide range of movements necessary for ambulation, balance, and athletic performance. Understanding its intricate anatomy, including the specific depressions and ligaments, is fundamental for anyone in exercise science and kinesiology.

Key Components of the Hip Joint:

• Femoral Head: The spherical, superior end of the femur, covered in articular cartilage, which fits into the acetabulum.
• Acetabulum: A cup-shaped depression located on the lateral aspect of the pelvis, formed by the fusion of the ilium, ischium, and pubis bones. It also features articular cartilage along its lunate surface, designed for smooth movement.

The Acetabular Fossa: The Specific Depression

Within the acetabulum, there is a distinct central depression that is not covered by articular cartilage. This non-articular area is the acetabular fossa. It is located inferior and medial to the lunate surface of the acetabulum, which is the articular portion.

The acetabular fossa serves as the primary attachment point for the ligament of the head of the femur, as well as housing the acetabular fat pad, which can absorb forces and provide lubrication. Its non-articular nature means it does not directly participate in weight-bearing or joint articulation.

The Ligament of the Head of the Femur (Ligamentum Teres Femoris)

The ligament of the head of the femur, often referred to as the ligamentum teres femoris or the round ligament, is the specific femoral ligament that attaches within the acetabular fossa.

Attachments:

• Proximal (Acetabular) Attachment: It originates from the acetabular fossa, specifically from the transverse acetabular ligament (which bridges the acetabular notch) and the margins of the fossa.
• Distal (Femoral) Attachment: It inserts into the fovea capitis femoris, a small, non-articular depression located on the center of the femoral head.

Function: While historically thought to provide significant stability to the hip joint, current understanding suggests its role in mechanical stability is relatively minor, especially compared to the strong capsular ligaments (iliofemoral, pubofemoral, ischiofemoral). Its primary functional importance lies in its role as a conduit:

• Vascular Conduit: The ligamentum teres contains the foveal artery (also known as the artery to the head of the femur or the obturator artery branch). This artery is crucial for supplying blood to the femoral head, particularly in children and adolescents. In adults, its contribution to the femoral head's blood supply diminishes as other sources (medial and lateral circumflex femoral arteries) become dominant, but it can still play a role in certain pathologies.
• Proprioception: Some studies suggest it may contain proprioceptive nerve endings, contributing to the body's sense of hip joint position and movement.

Clinical Significance

Understanding the acetabular fossa and the ligamentum teres femoris is vital due to their clinical implications:

• Avascular Necrosis of the Femoral Head: Disruption of the foveal artery, especially in children (e.g., in conditions like Perthes disease or following hip dislocations), can lead to avascular necrosis (death of bone tissue due to lack of blood supply) of the femoral head.
• Hip Dislocation: Traumatic hip dislocations can tear the ligamentum teres, potentially compromising the blood supply to the femoral head and increasing the risk of avascular necrosis.
• Hip Preservation Surgery: In some hip pathologies, surgical interventions may involve assessing or addressing issues related to the ligamentum teres and the acetabular fossa.

Beyond the Ligamentum Teres: Other Hip Ligaments

It's important to distinguish the ligamentum teres from the major extrinsic ligaments that provide the primary stability to the hip joint capsule. These robust ligaments reinforce the joint capsule and prevent excessive movement:

• Iliofemoral Ligament (Y-ligament of Bigelow): The strongest ligament in the body, preventing hyperextension of the hip.
• Pubofemoral Ligament: Prevents excessive abduction and hyperextension.
• Ischiofemoral Ligament: Prevents excessive internal rotation and hyperextension.

These ligaments are crucial for maintaining joint integrity and are the primary passive stabilizers of the hip, whereas the ligamentum teres has a more specialized role related to vascular supply and, to a lesser extent, proprioception.

Conclusion

The acetabular fossa is a specific, non-articular depression within the acetabulum that serves as the attachment site for the ligament of the head of the femur (ligamentum teres femoris). While the ligamentum teres plays a minor role in hip joint stability, its critical function lies in housing the foveal artery, which is vital for blood supply to the femoral head, particularly in early life. A thorough understanding of these intricate anatomical details is indispensable for fitness professionals, kinesiologists, and anyone dedicated to optimizing human movement and health.